Early life and family in Amsterdam; childhood interest in astronomy and telescope-building; undergraduate at Rijksuniversiteit te Leiden (W. deSitter, J. Woltjer), works at Leiden Observatory; growing interest in galactic research (Ejnar Hertzsprung, Jan Oort); contact with others at Leiden (Paul Ehrenfest, Hendrik Kramers). Assistantship at Rijksuniversiteit te Grn̲ingen, 1938; cooperative stellar catalog with Harvard University and Universitt̃ Hamburg. Life during the German Occupation, conditions in Leiden and Holland; the Resistance Movement; returns to Leiden, 1945. Begins work on thesis at end of war, continues Jacobus C. Kapteyn's interest in proper motion of helium star (Scorpio-Centaur association); compares Boss Catalog and FK Catalog for systematic errors (Oort). Discussion of postwar developments in time scale problem (Albrecht Unsl̲d, Victor Ambartsumian). To Yerkes Observatory, 1947; impressions of Yerkes and other American observatories: RR Lyrae variables (Otto Struve), 1947-1948; work on extension of cluster expansion (W. W. Morgan), 1952; work in Kenya on stellar positions (Maarten Schmidt), 1949-1950. Back to Yerkes, 1953-1957 (Bengt Strm̲gren, Gerard Kuiper, S. Chandrasekhar, A. Hiltner). Directorship of Kapteyn Laboratory, Groningen; organization of the Radio Foundation. Origins and development of European Southern Observatory; five-year term as Director. Views on development of astronomy in Holland (Antoine Pannekoek, Marcel Minnaert, Pieter van Rhijn); radio astronomy.